The present invention relates to a method for preparing lactam, which comprises an amination reaction using crystalline aluminosilicate zeolites as catalysts under the condition of gas phase in the presence of (a) lactone, (b) amine and/or ammonia and (c) water. The method of the present invention, which uses crystalline aluminosilicate zeolite catalysts, has many advantages including low reaction pressure, high yield per unit time, and short reaction time, etc.
Lactam, such as 2-pyrrolidone, N-alkylpyrrolidone, caprolactam etc., is used as a solvent or a polymeric monomer of high molecular compounds. Thus, developing an economic method for preparing lactam is a common industrial requirement.
For example, pyrrolidone may be synthesized by a hydrogenation and an amination reaction with succinic acid, succinic anhydride, maleic acid or maleic anhydride, etc.; caprolactam may be synthesized by a hydrogenation and an amination reaction with cyclohexanone. Moreover, lactam may also be synthesized by an amination of lactone and amine with a method of catalytic reaction or a method of non-catalytic reaction.
Regarding the method of non-catalytic liquid phase reaction, Japanese Patent Application Nos. Sho-47-21420 and Sho-49-20585 disclose a method of reacting an excessive amount of aqueous methylamine solution with xcex3-butyrolactone and generating N-methylpyrrolidone at a temperature of 200 to 300xc2x0 C. under 20 to 40 atm. In this method, methylamine is first dissolved in the water, and then reacted with xcex3-butyrolactone, which is effective for the selectivity of N-methylpyrrolidone. Japanese Patent Application No. Sho-51-42107 discloses a method of dissolving an excessive amount of methylamine in the water, and recycling methylamine in the reaction by water carrying methylamine. Japanese Patent Examined Publication Nos. Hei-6-78304 and Hei-7-10835 disclose an improved method of using secondary or tertiary amine for preparing N-substituted-2-pyrrolidone. However, such non-catalytic liquid phase reactions described above still have many disadvantages, including high-pressure operation and low yield per unit time (i.e., long reaction time), so that it does not yield a beneficial economic effect in the industrial process. Furthermore, in these reactions, industry needs to use large reactor equipment because of the high reaction pressure and the long retention time of the product in the reactor, so that its manufacturing cost is prohibitive.
Regarding the method of catalytic liquid phase reaction, Paul G. Rodewald et al. first proposed in U.S. Pat. No. 3,775,431 in 1973 a process by which lactone is reacted with primary amine and generates lactam using Zeolite X as catalysts. However, for example, in generating N-methylpyrrolidone, the yield of resultant products is still poor although the reaction temperature reaches 300xc2x0 C., the reaction pressure reaches 500 psig and an excessive amount of methylamine is used, such as where the molar ratio is over 30.
We, the inventors, have broadly and deeply studied the defects of the traditional technique, and found that an amination reaction of lactone and amine and/or ammonia using crystalline aluminosilicate zeolites as catalysts under the condition of gas phase may substantially decrease the reaction pressure of operation and increase the yield of products. We have hereby accomplished the present invention.
The present invention is related to a method for preparing lactam represented by the following formula (I): 
wherein R is C2-10 alkylene which may be optionally substituted with C1-6 alkyl or phenyl; Rxe2x80x2 is a hydrogen atom, C1-6 alkyl, C1-6 hydroxyalkyl or phenyl. The method for preparing lactam comprises an amination reaction using crystalline aluminosilicate zeolites as catalysts under the condition of gas phase in the presence of (a) lactone, (b) amine and/or ammonia and (c) water.
Lactone, the starting material used in the present invention, may be represented by the following formula (II): 
wherein the definition of R has the same meaning described above.
In the present invention, the example of C2-10 alkylene represented by R includes ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, etc. C2-10 alkylene represented by R may be optionally substituted with C1-6 alkyl or phenyl. The example of C1-6 alkyl as a substituent includes methyl, ethyl, propyl, butyl, pentyl, hexyl, etc.
The preferred example of lactone used in the present invention includes xcex2-propiolactone, xcex3-butyrolactone, xcex3-phenyl-xcex3-butyrolactone, xcex3-methyl-xcex3-butyrolactone, xcex3-phenyl-xcex3-methyl-xcex3-butyrolactone, xcex4-butyrolactone, xcex3-valerolactone, xcex3-caprolactone, xcex5-caprolactone, xcex4-hydroxyoctylic acid lactone, xcex4-hydroxynonylic acid lactone, xcex4-hydroxydecylic acid lactone, etc., more preferably xcex3-butyrolactone, xcex3-caprolactone and xcex5-caprolactone.
Amine, the starting material used in the present invention, may be primary, secondary or tertiary acyclic amine substituted with one to three C1-6 alkyl, C1-6 hydroxyalkyl or phenyl. While mono-, di- or tri-C1-6. alkylamine, mono-, di- or tri-C1-6 alkanolamine is preferred, the example includes mono-, di- or tri-methylamine, mono-, di- or tri-ethylamine, n-propylamine, n-butylamine, n-hexylamine, mono-, di- or tri-ethanolamine, etc.
The present invention utilizes crystalline aluminosilicate zeolites as catalysts for the amination reaction. The crystalline aluminosilicate zeolite has an excellent reactive effect in comparison with other conventional zeolite catalysts, such as mordenite (Na8Al8Si40O96.24H2O), Y-type zeolite, etc. In the crystalline aluminosilicate zeolite, silicon dioxide and aluminum oxide are in the ratio of (30 to 500):1, and the constraint index is 1 to 12. The preferred example of the crystalline aluminosilicate zeolite includes ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-34, ZSM-35, ZSM48, etc. ZSM-5 catalysts with three dimensional structures in which the pore size is from 5 to 6 angstrom between small pore molecular sieves (such as A-type zeolite, calcium magnesium zeolite, etc.) and large pore molecular sieves (such as octahedral zeolite, mordenite, etc.) is the most preferred. Therefore, the amination of the present invention is a heterogeneous reaction.
Lactone and amine and/or ammonia used in the amination reaction of the present invention must mix with water in a proper ratio in advance to use as the reactant. In the reactant, the amount of amine and/or ammonia may be more or less than the amount of lactone; in general, an excessive amount of amine and/or ammonia is preferably used.
The molar ratio of lactone and amine and/or ammonia used in the present invention usually ranges from (1:0.5) to (1:30), preferably from (1:1) to (1:10). The increase of the molar ratio of feeding lactone and amine and/or ammonia, such as the increase of 1:5 or more, may shorten the reaction time, as well as easily purify and separate the excessive amount of amine and/or ammonia from the product after the reaction. However, if the molar ratio is over the upper limit, the selectivity may become poor. If the molar ratio is below the lower limit, amine and/or ammonia become the limiting reagent, so that it is difficult to purify and separate the excessive amount of lactone from the product after the reaction.
The molar ratio of lactone and water used in the present invention usually ranges from (1:0.5) to (1:20), preferably from (1:2) to (1:6). If the molar ratio is below the lower limit, the conversion and selectivity of the reaction may obviously become poor. If the molar ratio is over the upper limit, the purification and separation of the product after the reaction may cost excessive amounts of time and energy, although the reaction is not directly affected.
The temperature of the amination reaction used in the present invention ranges from 180 to 400xc2x0 C., preferably 220 to 320xc2x0 C. In general, the selectivity of the reaction may be raised with the increase of the temperature. However, if the temperature is over 400xc2x0 C., undesired by-products may be yielded in addition to the resultant lactam. If the temperature is below 180xc2x0 C., the reaction may not be carried out rapidly enough to be effective.
Because the acidity of the crystalline aluminosilicate zeolite described above is stronger than aluminum oxide and the reactivity is also strong, the amination reaction of the present invention may be carried out at a pressure which does not destroy the configuration of the catalyst. The pressure used in the reaction usually ranges from 0 to 10 atm., preferably from 1 to 5 atm. While the increase of the pressure may slightly raise the conversion of lactone, the effect is not significant in comparison with other factors affecting the experiment.
The amination reaction of the present invention may be carried out in the fixed bed reactor, the fluid bed reactor, and the other heterogeneous gas phase reactor. If the fixed bed reactor is used, the crystalline aluminosilicate zeolite catalyst described above needs to form shapes for easy packing, such as in grains, tablets, etc.
The gas hourly space velocity (hereinafter sometimes abbreviated as GHSV) used in the amination reaction of the present invention may depend on the reaction of various lactone and amine and/or ammonia. In general, GHSV is 20 to 100000 hrxe2x88x921, preferably 2000 to 50000 hrxe2x88x921. If GHSV is over 100000 hrxe2x88x921, the reaction is not completed, and the conversion is poor. If GHSV is below 20 hrxe2x88x921, undesired by-products may easily result due to the lengthy time of contacting with the catalyst.